Successful positioning of locking screws in the base of a retaining intamedullary nail is a difficult and time-consuming undertaking. The most common procedure employs manual alignment with the aid of an x-ray-transmissive angle-gear system. The accuracy of this method depends on the skills of the operator. Also, it usually involves extensive exposure to radiation.
Elimination of the use of an x-ray machine is the object of the alignment devices described in German patent applications DE 4,306,724 and DE 4,414,177. However, the accuracy of these alignment devices is a function of the extent to which the intramedullary nail inserted in the bone has retained its original pre-insertion shape. These alignment devices cannot compensate for an implantation-induced bending of the nail nor any twisting between the top end and the base of the intramedullary nail. An investigation of implantation-induced deformation of solid intramedullary nails found that this is not an absolute prerequisite for accurate positioning; the twisting of solid nails is minimal and in practical application quite negligible whereas, on the other hand, there is considerable bending. It is this bending of the intramedullary nails that affects the accuracy of the aforementioned positioning devices. The results of this investigation were published in the September, 1996 issue of the journal, "Der Unfallchirurg" (The Accident Surgeon), under the title "ANALYSIS OF IMPLANTATION-INDUCED NAIL DEFORMATION AND X-RAY-MORPHOMETRIC STUDIES AS THE BASIS FOR A POSITIONAL ALIGNMENT DEVICE FOR DISTAL LOCKING WITHOUT AN X-RAY IMAGE INTENSIFIER".
An alignment device is also disclosed in Swiss patent CH 668,692. This device was designed for the purpose of permitting the axis of the hole(s) of the alignment device that is to be lined up with a hole in the distal base of the nail to be aligned with the axis of an existing hole in the distal base of a nail whenever the nail is bent or twisted between its proximal end and the holes in its distal base. This alignment device, however, requires the use of an x-ray machine. While it reduces the amount of the radiation needed, it cannot altogether do without it.
U.S. Pat. Nos. 5,281,224 and 5,433,720 describe positional alignment devices which seek to eliminate the need for an x-ray machine while at the same time tolerating some deformation of the nail upon insertion. These alignment devices are based on the concept of readjusting the alignment of the axes of the holes of the drill guide with the axes of the locking holes in the distal base of the nail using a metal detector. This metal detector uses electronic circuitry and generates a magnetic field. These inventions were sponsored by a company named ORTHOFIX S. R. L., but so far none of these alignment devices have been seen on the market.
Finally, ORTHOFIX S. R. L. has commercially introduced an alignment device in which, by means of a mandrel-shaped spacing sensor, so-called "direct contact" is possible with the anterior, forward edge of the distal base of the intramedullary nail. This alignment device is described in PCT application WO96/03085. Supposedly, this alignment device can be operated entirely without the aid of an x-ray machine, and it tolerates bends in the nail in the anteroposterior plane. In the mediolateral plane, however, the tolerable amount of nail bending is reduced to the contact surface of the positional stabilizing mandrel, which is relatively small. Furthermore, this alignment device is designed in a way that distal locking screws can be inserted only in a mediolateral orientation. Yet locking an intramedullary nail in only one single plane leaves it incomplete. For improved resistance to tilting, however, the intramedullary nails should preferably be secured along more than one single radial plane. Thus, the ORTHOFIX alignment device is deficient in this regard.